Shaft braking discs of the type having a unitary friction ring with annular bodies on both sides and cooling air channels therebetween, these channels being limited by ventilation ribs unitary with the annular bodies and extending radially, are known, e.g., from European Patent No. 87 071. In this type of construction, at least some of the ventilation ribs, uniformly spaced along the circumference, are extended radially inwardly as support spokes and connected by the latter to a hub seated on the shaft to be braked. The spokes have a width, in the axial direction, which diminishes smoothly in the radially inward direction from the friction ring to the hub. The spokes have no reinforcement in the circumferential direction, so that their cross sectional area diminishes radially inwardly correspondingly to their width.